Verify configured environment

Try compiling some C code, If it works then we're probably fine.
I don't even try to verify cross-compilation because I don't need it.
It should work, but that's not my problem right now.

.github/workflows/main.yml

@@ -22,3 +22,7 @@ jobs:
         run: npm install
       - name: Enable Developer Command Prompt
         uses: ./
+      - name: Compile and run some C code
+        run: |
+          cl.exe hello.c
+          hello.exe

hello.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+int main(int argc, char **argv)
+{
+	printf("Hello, world!\n");
+	return 0;
+}